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Author: Prof Gavin R Thomson

Introduction

Foot and mouth disease (FMD) is caused by viruses that belong to seven immunologically distinct serotypes of the genus Aphthovirus which is classified within the Picornaviridae family. The disease naturally affects cloven-hoofed animals although the severity of the resulting disease varies between different species. FMD viruses may rarely induce disease in other artiodactyls such as Bactrian camels (Camelus bactrianus) but apparently not dromedaries (C. dromedarius) and Indian- but not African elephants. The susceptibility of alpacas and llamas is disputed but, at worst, they only become infected under exceptional circumstances and have played no significant part in the maintenance and spread of FMD in South America. Some other mammalian species can be infected artificially, e.g. African elephants, mice and guinea pigs.

The disease is characterized by the development of vesicles in the mucosa of the mouth (with the exception of the ventral surface of the tongue) and the skin of the coronets and interdigital spaces of the feet. Lesions may also occur on the muzzle/snout. In dairy cattle it may cause teat lesions and severe mastitis. FMD rarely causes fatal illness — myocarditis in neo-natal animals being an exception — but the disease may be severely debilitating in intensively farmed livestock, pigs and cattle particularly, rendering intensive livestock farming unprofitable. In extensive farming systems the disease is often mild and most affected animals make an uneventful recovery within three weeks.

Although FMD viruses may spread quickly and efficiently, including over long distances via air currents when the epidemiological circumstances are suitable, in warm, dry climates where stocking rates are low its spread may be slow. Thus the frequently repeated claim that this is the most contagious disease of vertebrates is not altogether correct; rate of spread is variable and dependent on epidemiological circumstance.